1. Field of the Invention
This invention relates to a suspension system for a vehicle, and in particular, to an active suspension system.
2. Description of the Related Art
A conventional active suspension system is disclosed in, for example, Japanese Patent Publication No. 62-96113, laid open to the public on May 2, 1987, a European Patent Application, laid open to the public on Aug. 1, 1984 under a publication number 0114757 and U.S. Pat. No. 4,371,182, issued on Feb. 1, 1983. In the active suspensions as disclosed in the publications enumerated above, a cylinder device is provided for each vehicle wheel member between a vehicle boby member and a vehicle wheel member. By controlling the fluid supply/discharge to/from the cylinder device, the quantity of fluid in the cylinder device can be changed so that the vehicle suspension characteristics are changed.
In the active suspension system, the fluid pressure of each cylinder device is sensed, and warping of the vehicle body is computed based on the sensed pressures. Then, the fluid supply/discharge to/from the individual cylinder devices is controlled so as to suppress the warping of the vehicle body (hereinafter called warp control).
On the other hand, in the active suspension system, after the vehicle height displacement has been sensed, the fluid supply/discharge to/from the individual cylinder devices is controlled so as to set the vehicle height displacement to a desired value (hereinafter called vehicle height displacement control).
Since the warp control and the vehicle height displacement control are performed independently, both controls should be desirably coordinated.